# 13.4 sum of angles _1allr

Sum of the angles
The sum of the three angles in a triangle is 180°
The sum of the four angles in a quadrilateral is 360°

A+B+C=180°
D+E+F+G=360°
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Slide 1: Slide
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This lesson contains 10 slides, with interactive quizzes and text slides.

Lesson duration is: 50 min

## Items in this lesson

Sum of the angles
The sum of the three angles in a triangle is 180°
The sum of the four angles in a quadrilateral is 360°

A+B+C=180°
D+E+F+G=360°

#### Slide 1 -Slide

Calculating angles
You can use the sum of the angles and your knowledge of special triangles and quadrilaterals to calculate unknown angles.

#### Slide 2 -Slide

Calculating angles
Calculate the size of angle C.

#### Slide 3 -Slide

What size is angle C?
A
C=3608260=218°
B
C=82+60=142°
C
C=1808260=38°
D
C=3(82+60)=37°

#### Slide 4 -Quiz

Calculating angles
The angle sum of a triangle is 180°

C=1808260=38°

#### Slide 5 -Slide

Calculating angles
Calculate the size of angle G.

#### Slide 6 -Slide

What size is angle G?
A
G=245°
B
G=115°
C
G=65°
D
G=57.5°

#### Slide 7 -Quiz

Calculating angles
The angle sum of a quadrilateral is 360°
A rhombus has rotation and reflection symmetry, therefore the opposite angles are equal.

D=F=115°
G=E=2(360115115)=2130=65°

#### Slide 8 -Slide

Equal angles in triangle and quadrilaterals
Isosceles triangle: 2 angles (base angles) are the same size
Equilateral triangle: all 3 angles are the same size (60°)
Rhombus/Parallelogram: opposite angles are equal
Kite: 2 angles are the same size (on either side of the axis of symmetry)
Square/Rectangle: all 4 angles are the same size (90°)